PURPOSE: To prevent the reduction of the mechanical efficiency, generation of seizure, and the generation of cavitation erosion by fitting a bush having a plurality of static pressure holes in the circumferential direction and a throttle passage for the communication of the static pressure holes to a high pressure side, onto a cylinder bore part in which a plunger moves in reciprocation.

CONSTITUTION: A bush 4 is press-fitted onto the cylinder bore part 3 of the cylinder block 1 of a swash plate type plunger pump, and a plunger 3 is moved in reciprocation in the cylinder bore part 3 through the bush 4. On the bush 4, a plurality of static pressure holes 5 are formed at equal intervals in the circumferential direction, and each static pressure hole 5 communicates to the large diameter part 7 of the cylinder bore part 3 through a throttle passage 6 on the U-shaped sectional surface which is formed in the axial direction on the outer peripheral surface of the bush 4. When the plunger 2 moves in reciprocation in the cylinder bore part 3, the pressurized fluid sucked into the large diameter part 7 is introduced into each static pressure hole 5 through a groove 8 and a throttle passage 6, and the force in the radial direction which acts onto the plunger 3 in the cylinder bore part 3 is supported by the static pressure force in each static pressure hole 5.